1. Field of the Invention
The present invention relates to a wireless communications apparatus for use in a base station and a wireless terminal station forming a wireless system.
2. Description of the Background Art
Recent years, the security system has been known, which uses wireless transmission between a base station including a transmitter/receiver and a terminal station including a sensor device, for example, to transmit sensor-detected information from the terminal station to the base station. For such a system, the Association of Industries and Businesses, a corporate juridical person in Japan, provides the standard for wireless communications equipment for use in the wireless stations of low-power security systems.
Wireless communications equipment for use in such a wireless station, for example, is composed of a wireless transmitter/receiver and a controller, implementing a crime prevention system or an emergency alert system. In such systems, a base station transmits and receives data to and from a wireless terminal device staying in an area covered by the base station, and repeats its receiving operation at predetermined time intervals. When the wireless terminal device intends to send data, it shall send and deliver the data to the base station during the receiving operation of the base station.
However, the wireless station of the type described above is composed of a transmitter/receiver and a controller which are adapted to transmit and receive data only when both of the transmitter/receiver and the controller are constantly operative, thus not being suitable for saving power consumption. For example, in an application in which both base and terminal stations are battery-powered, much more reduction in power consumption is required.
In Japanese patent laid-open publication No. 163452/1997, an information processor is disclosed in which it is determined whether or not the value of an electric field strength is higher than a required value to turn the wireless communication function on or off. However, in an application where the communication unit and the control unit are fabricated on semiconductor chips separated from each other, satisfactory reduction in power consumption was not attained.